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Upper-Mantle Velocity Heterogeneity of Eastern Tibetan Plateau from Teleseismic P-Wave Tomography and Its Tectonic Implications

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Journal of Earth Science 2023年第1期34卷 280-290页

作者： Shahpara Sheikh Dola Junmeng Zhao Heng Zhang Shunping Pei State Key Laboratory of tibetan plateau Earth System Environment and Resources(TPESER)Institute of Tibetan Plateau ResearchChinese Academy of SciencesBeijing100101China University of Chinese Academy of Sciences Beijing100049China Nuclear Safety Security&Safeguards Division(NSSSD)Bangladesh Atomic Energy Regulatory Authority(BAERA)Dhaka1207Bangladesh

An attempt has been made to reveal the upper mantle velocity structure of the Eastern Tibetan Plateau using 628 teleseismic events recorded from 2003 to 2009 at 95 stations.A total of 8 532 Pwave arrival time residuals were inverted by using the FMTOMO(fast marching tomography) software package.Tomographic results show upper mantle velocity heterogeneity in many aspects.In the southern part visible high velocity anomaly is denoted as the Indian lithosphere.This part seems to be affected by slab tearing at 940E longitude as it is located on the eastern Himalayan syntaxis(EHS).The high velocity zone down to 500 km depth in the northern part could be the Asian lithosphere.At the central part some high velocity anomalies can be identified as detached patches of the lithosphere,surrounded by low velocity anomalies.These anomalies are the potential to create thermal convection and trigger plateau uplift or plateau growth.Sudden velocity change occurs on both sides of patches where low velocity anomaly is visible in between patches and Bangong-Nujiang suture even in between Songpan-Ganzi terrain and Asian Plate.In both cases intense low velocity zone spread down to 500 km.The depth range of low velocity anomalies in between two plates observed from 200 to-500 km.Hence the low velocity anomalies detected in our results may reflect either the hot asthenosphere upwelling or the mantle wedge due to the presence of the cold lithosphere.

关键词： upper mantle tomography Eastern Tibetan Plateau FMTOMO velocity heterogeneity

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Paleoglacial and paleoclimate reconstructions during the global Last Glacial Maximum in the Longriba area, Eastern Tibetan Plateau

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Journal of Mountain Science 2021年第2期18卷 307-322页

作者： YANG Wei-lin HAN Ye-song PENG Xu RAN Ze-ze LIU Qing LIU Geng-nian College of Urban and Environmental Sciences Peking UniversityBeijing 100871China

Owing to the remoteness of the Longriba area and the lack of dating records,it is extremely challenging to reconstruct the chronology and extent of the paleoglaciers in this area.In this paper,we combined limited observational data with automated modelling for paleoglacial reconstructions.We first identified a broadly distributed paleoglacier from satellite imagery and field investigation based on the sediment-landform assemblage principle and dated it to 23.1±1.4~19.5±1.2 ka by ^(10)Be exposure dating,corresponding to the global Last Glacial Maximum(gLGM).Then,we reconstructed the extent and ice surface of 171 paleoglaciers formed during the similar period based on geomorphological evidence and‘ice surface profile’modelling.The results showed that the paleoglacial coverage was 426.5 km2,with an ice volume of 38.1 km^(3),in the Longriba area.The reconstructed equilibrium line altitudes(ELAs)based on modelled ice surfaces yielded an average of 4245±66 m above sea level(asl),~725±73 m lower than the present ELA(4970±29 m asl).The temperature was~5.51-6.68℃lower,and the precipitation was~30-34%less in Longriba,during the gLGM compared to the present day.This glacial advance was mainly driven by colder climate that was synchronous with Northern Hemisphere cooling events.

关键词： Ice surface profile ^(10)Be surface exposure dating Paleoglacial reconstruction Paleoclimate reconstruction Global Last Glacial Maximum Eastern Tibetan Plateau

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Strong earthquake clustering around the Eastern Tibetan Plateau after the 2008 MW7.9 Wenchuan earthquake

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Science China Earth Sciences 2020年第7期63卷 999-1012页

作者： Duyuan XU Jie XIAO Jiankun HE Weimin WANG Key Laboratory of Continental Collision and plateau Uplift Institute of Tibetan Plateau ResearchChinese Academy of SciencesBeijing 100101China CAS Center for Excellence in tibetan plateau Earth Sciences Chinese Academy of SciencesBeijing 100101China College of Earth and Planetary Sciences University of Chinese Academy of SciencesBeijing 100049China

After the 2008 M_W7.9 Wenchuan earthquake,the Eastern Tibetan Plateau experienced a series of M_W>6.0 earthquakes,including the 2013 M_W6.6 Lushan,2014 M_W6.1 Kangding and 2017 M_W6.5 Jiuzhaigou events.Based on available constraints,we build a three-dimensional viscoelastic finite element model to calculate Coulomb failure stress caused by these strong earthquakes.In this model,the geometry and slip vector of the initial rupture zone of each earthquake are used to better evaluate the earthquake-related stress projection.Considering reasonable ranges of viscosities for the crust and upper mantle in different tectonic units,numerical results show that after the Wenchuan earthquake,the coseismic Coulomb failure stress change at the hypocenters of the subsequent earthquakes increased to approximately+0.012–+0.040,+0.01–+0.03,and+0.008–+0.015 MPa,respectively.With viscoelastic relaxation of the lower crust and upper mantle,the Coulomb failure stress change at the hypocenters of these earthquakes accumulated to about+0.014–+0.042,+0.016–+0.036,and+0.003–+0.007 MPa just before their occurrence.This suggests that the Wenchuan earthquake indeed triggered or hastened the occurrence of the Lushan,Kangding and Jiuzhaigou events,supporting that strong earthquake clustering around the Eastern Tibetan Plateau could be related to stress interaction between the seismogenic faults.Besides,~94%and^6%of the stress increase around(and before the occurrence of)the Kangding earthquake were contributed by the Wenchuan event and the Lushan event,respectively;the positive Coulomb failure stress change at the Jiuzhaigou earthquake hypocenter was related to coseismic slip partitioning of the Wenchuan earthquake.This means that stress interaction among the earthquakes could be controlled by the combined effect of stress of the previous events and by the complexity of earthquake ruptures.Thus,in researches on the earthquake-triggering mechanism,special attentions should be paid on both details of the rupture model and multiple factors of prev

关键词： Earthquake clustering Viscoelastic stress triggering Finite element modeling Wenchuan earthquake Eastern Tibetan Plateau

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Last Deglacial Soft-Sediment Deformation at Shawan on the Eastern Tibetan Plateau and Implications for Deformation Processes and Seismic Magnitudes

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Acta Geologica Sinica(English Edition) 2019年第2期93卷 430-450页

作者： ZHONG Ning JIANG Hanchao LI Haibing XU Hongyan SHI Wei ZHANG Siqi WEI Xiaotong Institute of Geology Chinese Academy of Geological Sciences Key Laboratory of Deep-Earth Dynamics Ministry of Natural Resources State Key Laboratory of Earthquake Dynamics Institute of GeologyChina Earthquake Administration College of Earth Sciences University of Chinese Academy of Sciences College of Geosciences and Resources China University of Geosciences

The eastern margin of the tibetan plateau is characterized by frequent earthquakes; however, research of paleo-earthquakes in the area has been limited^ owing to the alpine topography and strong erosion. Detailed investigations of soft-sediment deformation(SSD) structures are valuable for understanding the trigger mechanisms, deformation processes, and the magnitudes of earthquakes that generate such structures, and help us to understand tectonic activity in the region. To assess tectonic activity during the late Quaternary, we studied a well-exposed sequence of Shawan lacustrine sediments, 7.0 m thick, near Lake Diexi in the upper reaches of the Minjiang River. Deformation is recorded by both ductile structures(load casts, flame structures,pseudonodules, ball-and-pillow structures, and liquefied convolute structures) and brittle structures(liquefied breccia, and microfaults). Taking into account the geodynamic setting of the area and its known tectonic activity, these SSD structures can be interpreted in terms of seismic shocks. The types and forms of the structures,the maximum liquefaction distances, and the thicknesses of the horizons with SSD structures in the Shawan section indicate that they record six strong earthquakes of magnitude 6-7 and one with magnitude >7. A recent study showed that the Songpinggou fault is the seismogenic structure of the 1933 Ms7.5 Diexi earthquake. The Shawan section is located close to the junction of the Songpinggou and Minjiang faults, and records seven earthquakes with magnitudes of ?7. We infer,therefore, that the SSD structures in the Shawan section document deglacial activity along the Songpinggou fault.

关键词： lacustrine sequence soft-sediment deformation(SSD) deformation process earthquake magnitude Shawan Eastern Tibetan Plateau

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Relationship between the regional tectonic activity and crustal structure in the Eastern Tibetan Plateau discovered by gravity anomaly

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Earthquake Science 2016年第2期29卷 71-81页

作者： Xiao Xu Rui Gao Xiaoyu Guo Key Laboratory of Earthprobe and Geodynamics MLR Instituteof GeologyChinese Academy of Geological Sciences Sinoprobe Center Chinese Academy of Geological Sciences

The Eastern Tibetan Plateau has been getting more and more attention because it combines active faults,uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus,a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative（THD） had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks,including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the SongpanGarze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion,which is coincident with the flowing direction indicatedfrom the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the Eastern Tibetan Plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault.

关键词： Eastern Tibetan Plateau Tectonic activity Crustal structures Gravity anomaly

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Three dimensional velocity model and its tectonic implications at China Seismic Experimental Site, eastern margin of the tibetan plateau

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Science China Earth Sciences 2024年第7期67卷 2268-2290页

作者： Jianping WU Yan CAI Wei WANG Weilai WANG Changzai WANG Lihua FANG Yaning LIU Jing LIU Institute of Geophysics China Earthquake Administration Beijing Baijiatuan Earth Science National Observation and Research Station Beijing Earthquake Agency

The China Seismic Experimental Site(CSES) is located at the intersection of the tibetan plateau, South China Block,and Indian Plate and has complex geological settings and intense crustal deformation, making it one of the most seismically active areas in Chinese mainland. A high-resolution, three-dimensional(3D) crust-mantle velocity structure is crucial for understanding seismotectonic environments, lithospheric deformation mechanisms, and deep dynamic processes. We first constructed a high-vertical-resolution 3D initial velocity model using the joint inversion of receiver functions and surface waves and then obtained a 3D P-and S-wave velocity model(CSES-VM1.0) with the highest lateral resolution of 0.25° for the CSES using double-difference tomography. Owing to the limitations of the Sn observation data, the resolution of the S-wave velocity model in the lower crust and upper mantle was reduced, making it closer to the initial model provided by joint inversion. A comparison with explosive-source seismic data showed that the synthetic P-wave first-arrival travel times of the new model were closer to the observations than those of the previous velocity models. The velocity cross-sections across the source areas of the 2022 Lushan MS6.1 and Ludian MS6.8 earthquakes reveal that the former earthquake occurred near a weak contact zone between the tibetan plateau and Sichuan Basin, and the rupture of the latter earthquake occurred in a granitic area, with the northern end blocked by rigid high-velocity bodies. A clear high-velocity anomaly zone is distributed along the western margin of the Yangtze Block, revealing the spatial distribution of Neoproterozoic intermediate-basic intrusions. This high-velocity zone significantly controls the morphology of fault zones and influences the rupture processes of major earthquakes. Two northeast-southwest and north-south trending high-velocity anomalies were found near Panzhihua, potentially related to Neoproterozoic and Middle-Late Permian intermediate-basic intrusions. The im

关键词： Eastern Tibetan Plateau China Seismic Experimental Site Yangtze Block Velocity model Double-difference tomography

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Dextral-Slip Thrust Faulting and Seismic Events of the Ms 8.0 Wenchuan Earthquake,Longmenshan Mountains,eastern Margin of the tibetan plateau

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Acta Geologica Sinica(English Edition) 2009年第4期83卷 685-693页

作者： WU Zhenhan DONG Shuwen Patrick J. BAROSH ZHANG Zuoheng LIAO Huaijun Institute of Geomechanics CAGS Beijing 100081 China Chinese Academy of Geological Sciences Beijing 100037 China P.J. Barosh ＆ Associates 103 Aaron Ave. Bristol RI 02809 USA China Geological Survey Beijing 100037 China Geological Brigade 316 Chongqing 401147 China

Dextral-slip thrust movement of the Songpan-Garze terrain over the Sichuan block caused the Ms 8.0 Wenchuan earthquake of May 12, 2008 and offset the Central Longmenshan Fault （CLF） along a distance of -250 km. Displacement along the CLF changes from Yingxiu to Qingchuan. The total oblique slip of up to 7.6 m in Yingxiu near the epicenter of the earthquake, decreases northeastward to 5.3 m, 6.6 m, 4.4 m, 2.5 m and 1.1 m in Hongkou, Beichuan, Pingtong, Nanba and Qingchuan, respectively. This offset apparently occurred during a sequence of four reported seismic events, EQ1-EQ4, which were identified by seismic inversion of the source mechanism. These events occurred in rapid succession as the fault break propagated northeastward during the earthquake. Variations in the plunge of slickensides along the CLF appear to match these events. The Mw 7.5 EQ1 event occurred during the first 0-10 s along the Yingxiu-Hongkou section of the CLF and is characterized by 1.7 m vertical slip and vertical slickensides. The Mw 8.0 EQ2 event, which occurred during the next 10-42 s along the Yingxiu-Yanziyan section of the CLF, is marked by major dextralslip with minor thrust and slickensides plunging 25°-35° southwestward. The Mw 7.5 EQ3 event occurred during the following 42-60 s and resulted in dextral-slip and slickensides plunging 10° southwestward in Beichuan and plunging 73° southwestward in Hongkou. The Mw 7.7 EQ4 event, which occurred during the final 60-95 s along the Beichuan-Qingchuan section of the CLF, is characterized by nearly equal values of dextral and vertical slips with slickensides plunging 45°-50° southwestward. These seismic events match and evidently controlled the concentrations of landslide dams caused by the Wenchuan earthquake in Longmenshan Mountains.

关键词： Ms 8.0 Wenchuan earthquake co-seismic slip slickensides seismic events Central Longmenshan Fault Eastern Tibetan Plateau

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Co-Seismic Surface Rupture and Recurrence Interval of Large Earthquakes along Damaoyaba-Litang Segment of the Litang Fault on the eastern Margin of the tibetan plateau in China

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Journal of Earth Science 2021年第5期32卷 1139-1151页

作者： Shiyuan Wang Rongjun Zhou Mingjian Liang Shao Liu Nina Liu Jianyu Long Sichuan Earthquake Agency^Chengdu 610041 China School of Geological Engineering and Geomatics Chang'an UniversityXi'an 710054China

The Litang fault is a left-lateral secondary shear zone in the Sichuan-Yunnan active block that accommodates the tectonic deformation associated with the eastward extrusion of the upper crust of the tibetan plateau. Based on 1 : 50 000 geological mapping of active faults, the Litang fault consists of three geometric segments, the Cuopuhu, Damaoyaba, and Litang segments, in the west of Litang, which are divided by the of Haizi Mountain uplift and the wide-angle bending and branching of the fault near Jinchanggou. This study also identifies the surface rupture of the A.D. 1890 earthquake, which is distributed intermittently along the ~28 km long Damaoyaba segments and ~25 km long Litang segments. The maximum horizontal displacement is 4.1 m along Damaoyaba segments, and 4 m along Litang segments. The rupture involves typical left-lateral shear movement. The two ruptures are divided by discontinuous segments or gaps that are ~18 km long;thus, the total surface rupture is approximately 71 km long. The estimated moment magnitude was M_(w)7.3±0.1. A comprehensive analysis of data obtained from 5 trenches excavated along the Damaoyaba and Litang segments and the trench data by Xu et al.(2005) identifies age constraints of the 4 most recent paleoseimic events occurred B.C. 1468±54–1340±25, B.C. 52±25–A.D. 76±47, A.D. 1115±90, and A.D. 1890, respectively. The recurrence intervals are 1 415±80, 1 104±104, and 775±90 a, which are consistent with quasi-periodic earthquake recurrence behavior. The average recurrence interval is 1 098±112 a.

关键词： Litang fault surface rupture active fault recurrence intervals paleoearthquake Eastern Tibetan Plateau

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A Late Quaternary Climate Record Based on Multi-Proxies Analysis from the Jiaochang Loess Section in the Eastern Tibetan Plateau,China

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Acta Geologica Sinica(English Edition) 2007年第6期81卷 1087-1096页

作者： BAI Song TANG Ya WANG Chengshan HUANG Chengmin Department of Environmental Science and Engineering School of Architecture and Environment Sichuan University Chengdu 610065 China University of Geosciences Beijing 100083 China

We compared the stable carbon isotopic records from a loess transect of the Jiaochang in the Eastern Tibetan Plateau, spanning the last -21,000 years, with multiproxy data for pedogenesis, including magnetic susceptibility, clay fraction, Fed/Fet ratio, carbonate and total organic carbon content, in order to probe the mechanisms of δ^13C values of organic matter and Late Quaternary climate variations in the Eastern Tibetan Plateau. Our results indicate that there is no simple relationship between δ^13C of organic matter and summer monsoon variations. The change in δ^13C values of organic matter （in accordance with the ratios of C3 to C4 plants） results from the interaction among temperature, aridity and atmospheric pCO2 level. Drier climate and lower atmospheric pCO2 level contribute to positive carbon isotopic excursion, while negative carbon isotopic excursion is the result of lower temperature and increased atmospheric pCO2 level. Additionally, our results imply that the tibetan monsoon may play an important role in climate system in the eastern Tibet plateau, which specifically reflects frequently changing climate in that area. The results provide new insights into the forcing mechanisms on both the δ^13C values of organic matter and the local climate system.

关键词： Eastern Tibetan Plateau Jiaochang loess carbon isotope last glacial Late Quaternary

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The Impact of Atmospheric Heat Sources over the Eastern Tibetan Plateau and the Tropical Western Pacific on the Summer Rainfall over the Yangtze-River Basin

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Advances in Atmospheric Sciences 2006年第1期23卷 149-155页

作者：简茂球乔云亭袁卓建罗会邦 Research Center for Monsoon and Environment/Department of Atmospheric Sciences Sun Yat-sen (Zhongshan) UniversityGuangzhou 510275

The variability of the summer rainfall over China is analyzed using the EOF procedure with a new parameter （namely, mode station variance percentage） based on 1951-2000 summer rainfall data from 160 stations in China. Compared with mode variance friction, the mode station variance percentage not only reveals more localized characteristics of the variability of the summer rainfall, but also helps to distinguish the regions with a high degree of dominant EOF modes representing the analyzed observational variable. The atmospheric circulation diagnostic studies with the NCEP/NCAR reanalysis daily data from 1966 to 2000 show that in summer, abundant （scarce） rainfall in the belt-area from the upper-middle reaches of the Yangtze River northeastward to the Huaihe River basin is linked to strong （weak） heat sources over the Eastern Tibetan Plateau, while the abundant （scarce） rainfall in the area to the south of the middle-lower reaches of the Yangtze River is closely linked to the weak （strong） heat sources over the tropical western Pacific.

关键词： heat sources Eastern Tibetan Plateau tropical western Pacific summer rainfall Yangtze River basin

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